With Milsim games I'd like to see a much longer "you're dead" timing...but we've done some 1-life type scenarios and they're quite fun. Really depends on the guys and how much space you've got to work with.
In 1-life type scenarios with enough space to negotiate a precise mission objective is really fun if guys keep their heads. The scenario may span many hours or may finish up really quickly...it just depends on how it plays out. For the ones I've seen like that...even the "losers" are ok with it because really things could have gone either way.
TBH...in games with medics and quick respawns I'd admit to throwing caution to the wind with my "life" since the game dynamics turn more to who can "resupply" most efficiently to overwhelm the other side. Reminds me more of 1918'ish tactics of throwing guys into a meatgrinder and wearing down the other side until they tire out. Sure there's still consequences to getting shot...but they're either minor or readily managed tactically.
Points taken that you want to keep things fun for guys and burning them out endlessly with hiking back and forth to respawns really sucks the wind out of guys, especially in the latter timings.
It all comes down to the guys though. Some can get their heads around the intent of the rules/game...others can't or willfully disregard things because it's "hard" or "not fun". Aside from the latter guys, from all the games I've seen (of any type) the only issues that arise are ones when the expectations aren't clear and common.
Setting the rules so that you cannot go to respawn (or start your "bleed out" timer with medic rules) until the immediate firefight has completely finished is a good way to accomplish things. It also supports games where you're collecting "kill cards" or whatnot...since the dead guys don't get up and walk off before the fight is done. It might be a long wait if the area is strongly contested...but that's the cause and effect part of things. Having medics kick in afterwards will help with avoiding long hikes and losing people on respawns.